In general, a fuel injection valve includes a nozzle having multiple nozzle holes. The fuel injection valve injects fuel directly into an internal combustion engine through the nozzle holes. The nozzle is directed from a cylinder head toward a piston of the engine. In recent years, it is requested to enhance output power and reduce emission in an engine. Therefore, it is necessary to efficiently form a mixture of intake air and fuel injected from the fuel injection valve into the cylinder. In particular, it is important to efficiently utilize intake air and efficiently burning injected fuel in the cylinder.
According to JP-A-2003-227444, fuel is injected at an early timing in an intake stroke, so that mixture of intake air and injected fuel is further accelerated. In addition, penetration of injected fuel is maintained, so that injected fuel is restricted from being adhered onto a wall surface of the cylinder. Thus, fuel is restricted from being unburned.
According to JP-A-2004-28078, two sprays are formed vertically with respect to the axial direction of the cylinder, so that mixture of air and fuel is accelerated in the cylinder.
However, in the operation of JP-A-2003-227444, intake air fluctuates in flow direction and flow amount corresponding to an operating condition of the engine. Consequently, mixture of intake air and fuel is apt to be unstable.
According to JP-A-2004-28078, mixture of air and fuel is accelerated in a limited region, in which two sprays are formed in the cylinder. Consequently, intake air may be partially unburned in the cylinder.